The present invention refers to an assembly which is constituted by a fuel rail made of plastic material with a heating system. The said rail is employed in cold start auxiliary devices of internal combustion engines which consume fuels with an elevated specific vaporization heat, for example, alcohol.
In the last few years a great popularization of vehicles that use simultaneously more than one fuel has occurred, for example, gasoline and alcohol/ethanol. These vehicles, when they operate with alcohol as fuel, usually need an additional fuel tank dedicated to an initial injection of gasoline in order to start in cold climates. This is due to the fact that alcohol presents a high specific vaporization heat when compared to gasoline. Based on this physical-chemical limitation of alcohol and with the objective of eliminating the additional gasoline tank, vehicle manufacturers have developed cold starting devices for alcohol which aid the combustion process through the pre-heating of the fuel.
A cold start device is generally fixed in an upper region of the engine block and is, as a rule, constituted by a fuel rail which has injection valves, elements for heating the fuel, ducts for the passage of fuel and their respective couplings. The said ducts of the rail, already known by the state of the art, are made of steel, especially, stainless steel. This is due to the fact that alcohol is highly corrosive. The fact that the ducts are made of metal elevates the production costs for the assembly, as well as, contributing to an increase in the vehicles weight. A fuel rail with heating from the state of the art can be verified, for example, from the document WO 2006/130938.
Due to the problem of cost and weight cited above, it was necessary to develop alternative materials, especially, for the confection of ducts for said rail with a heating system. One of the alternatives is the use of a plastic material in place of metal, with the objective of significantly reducing costs and the total weight of the device associated with such change.
This change presents, however, some drawbacks for its implementation. The first is related to the use of heating elements which reach, as a rule, temperatures which could damage the plastic material. A second difficulty is linked to the confection of the rail with a single piece of plastic material with a mold that allows maintaining its complex geometry resulting from its functional characteristics known by the state of the art and that, at the same time, allows a rapid and economical plastic injection process.
In the state of the art there are no rails which aggregate, on one hand low cost and reduced weight of a rail made of plastic material and, on the other which manages to promote an adequate heating of the fuel. Such type of rail can be seen in document US 2009/199822 A1 which comprises different parts to be assembled together (which comprises security due to leakage of fuel) and also does not guarantee proper start-up of an engine when heating the fuel since due to its geometry will have to heat all the fuel inside the rail.
It is worth observing that the production process for plastic material elements must be done, preferably, in a single injection step. Otherwise, a later fitting of several components must be undertaken, which can result in a loss of the confiability of the rail. It must be observed that the smaller the number of components, the greater the safety, since the chances of a fuel leak is smaller.
The formation of a rail made of plastic material, preferably, in a single piece which attends to the complex geometry necessary to attain an ideal heating of the fuel is one of the objectives of the present invention. In the metal rails of the state of the art, what increases their total cost is the connection of its main external elements, constituted by a main tube and by two secondary ducts. This connection is made, generally, through a welding process, where entire metallic elements, of innumerous shapes, are united by a weld bead. It is interesting to observe that in the metal rail of the state of the art, in order to have a correct flow of fuel with adequate heating, it is necessary that the main tube is positioned in a substantially lower inferior part of the assembly. The shape of the heated rail of the state of the art can, therefore, interfere in the standard layout of an engine, eventually creating obstacles to its installation in the assembly line due to the difficulty of access for tools.